I had this same problem and I'm not obese at all. I found the solution to this problem with the following boxer briefs or compression shorts:
Speedo Axcelerate Compression Cycle Short (451003) has been discontinued and you only can buy it at Ebay-
Warrior Vaportek Compression Shorts (Navy or Black, don't buy the white, fabric is crappy)
Hope your husband solve this problem, the "inner thighs chafing" was a real nightmare to me and lasted 10 years of my life.
Tell me if you have any questions.